A conventional apparatus for recording and reproducing an information signal on and from a tape-shaped recording medium such as a video tape, an audio tape, etc., for example, a video tape recorder, is arranged as shown in FIG. 8. That is, a cylindrical rotary drum, which is equipped with video heads, is installed at a predetermined angle of inclination to a chassis board so as to record an information signal along linear tracks on a video tape by helical scanning.
In general, a plurality of tape guides and a pair of slant guide posts are provided around the rotary drum and a fixed drum for the purpose of accurately guiding a video tape to the lead of the fixed drum.
Recording and reproduction of an information signal with respect to a video tape are effected by traveling of the video tape along the lead of the fixed drum which is caused by rotation of a take-up reel (and a supply reel) and the rotary drum.
During the traveling, the video tape slides in contact with the surfaces of the stationary tape guides and the lead surface of the fixed drum, so that the video tape is subjected to frictional force produced by the contact sliding. When the frictional force caused by the contact sliding increases, the video tape cannot smoothly travel. As a result, the video tape may cause jamming. In the worst case, the video tape may be damaged.
Therefore, the conventional practice is to employ an aluminum alloy as a material for a sliding member 1, such as the fixed drum, stationary tape guides, etc., on which a video tape T slides, as shown in FIG. 5. Further, a large number of projections 1a are formed on the surface of the sliding member 1 to provide a configuration that reduces the area of contact with the video tape T, thereby minimizing frictional force produced between the video tape T and a part (sliding member 1) on which the video tape T slides.
However, in the conventional studies on the friction of the sliding member 1, notice has been taken of only the damage given to the tape T and how the coefficient of friction varies according to the number of times of sliding performed by the tape T, and studies have heretofore been conducted only from the mechanical point of view, for example, from the viewpoint of machining accuracy, easy machinability and hardness. Such studies have been satisfactory for the surface properties and tension of conventional tapes. However, as the surface properties of tapes improve and the tape tension decreases as in the present state of art, the following problems arise:
It has become clear that as the surface properties of the tape T improve and the tension of the tape T decreases, adsorbed water H which is present at the interface between the tape T and the sliding member 1 has a large effect on the traveling of the tape T. More specifically, by observation of the relationship between the layer thickness of adsorbed water H on the one hand and the temperature and humidity on the other when water molecules are physically adsorbed on the tape surface, it has been found that the layer thickness of adsorbed water H increases as the temperature and humidity rise, as shown in FIG. 6.
In general, during traveling, the tape T contacts the tips of the projections 1a of the sliding member 1 to form contact portions a of two metallic materials, as shown in FIG. 5. Friction occurs when the contact portions a are sheared. According to the characteristics shown in FIG. 6, as the temperature and humidity rise, the layer thickness of adsorbed water H increases, and hence bonded portions b of adsorbed water are produced around the contact portions a of the metallic materials. Accordingly, sliding of the tape T under high-temperature and high-humidity conditions involves not only shearing of the contact portions a of the metallic materials but also shearing of the bonded portions b of adsorbed water H. This means that frictional force (coefficient of friction) rises.
Let us show one experimental example. In this experiment, two different kinds of video tape, shown in Table 1 below, were moved past a conventional sliding member 1 made of an aluminum alloy to measure how the coefficients Y of friction of the two video tapes with respect to the sliding member 1 vary with the change of the relative humidity (the ambient temperature: 40.degree. C.).
TABLE 1 ______________________________________ Surface roughness Maximum roughness Average roughness Rmax Ra ______________________________________ Medium Tape A 300 nm 20 nm Tape B 50 nm 4 nm ______________________________________
The results of the experiment are shown in FIG. 7. As will be understood from the experimental results, with regard to the coated tape, which has a relatively high surface roughness, the friction coefficient Y is approximately constant throughout the entire humidity range, whereas, regarding the evaporated tape, which has a relatively low surface roughness, the friction coefficient Y rapidly rises from the region of humidity 78% and it jumps up to 0.85 at a high humidity in the region of humidity 94%.
Accordingly, the prior art suffers from the problem that when the VTR is operated under high-temperature and high-humidity conditions, the coefficient of friction occurring between the video tape T and the sliding member 1 rapidly rises, and as a result, the video tape T sticks to the sliding member 1, making it impossible to ensure the favorable traveling of the tape T.
In view of the above-described problems of the prior art, it is an object of the present invention to provide an apparatus for recording and reproducing a tape-shaped recording medium, which is capable of minimizing the effect of adsorbed water present at the interface between the tape and a sliding member and hence enables the tape to travel stably without sticking to the sliding member even under conditions close to moisture condensational conditions.